[MINOR] [BUILD] Declare ivy dependency in root pom.

Without this, any dependency that pulls ivy transitively may override
the version and potentially cause issue. In my machine, the hive tests
were pulling an old version of ivy, and subsequently failing with a
"NoSuchMethodError".

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #5893 from vanzin/ivy-dep-fix and squashes the following commits:

ea2112d [Marcelo Vanzin] [minor] [build] Declare ivy dependency in root pom.

core/pom.xml

@@ -273,7 +273,6 @@
     <dependency>
       <groupId>org.apache.ivy</groupId>
       <artifactId>ivy</artifactId>
-      <version>${ivy.version}</version>
     </dependency>
     <dependency>
       <groupId>oro</groupId>

pom.xml

@@ -416,6 +416,11 @@
         <artifactId>commons-math3</artifactId>
         <version>${commons.math3.version}</version>
       </dependency>
+      <dependency>
+        <groupId>org.apache.ivy</groupId>
+        <artifactId>ivy</artifactId>
+        <version>${ivy.version}</version>
+      </dependency>
       <dependency>
         <groupId>com.google.code.findbugs</groupId>
         <artifactId>jsr305</artifactId>